The present invention relates to a vacuum-assisted brake-force booster for a motor-vehicle braking system with                a force-input member which is capable of being coupled with a brake pedal,        a control-valve device which is capable of being actuated in accordance with a displacement of the force-input member,        a tandem chamber arrangement, with a first and a second working chamber and with a first and a second vacuum chamber and with        a force-output member for delivering an actuating force to a master-brake-cylinder arrangement,wherein the first working chamber and the first vacuum chamber are separated from one another via a first movable wall, and the second working chamber and the second vacuum chamber are separated from one another via a second movable wall, and in each instance are optionally capable of being connected to one another via the control-valve device andwherein at least one pneumatic connecting element is provided, via which the first working chamber is permanently connected to the second working chamber.        
A vacuum-assisted brake-force booster of such a type is known from the state of the art.
For instance, document DE 29 42 024 A1, and corresponding UK Patent Application No. GB 2 034 429 A, both of which are incorporated by reference herein, presents in FIG. 3 a vacuum-assisted brake-force booster with a tandem chamber arrangement. With this vacuum-assisted brake-force booster a pneumatic connection between corresponding working chambers of the tandem chamber arrangement is obtained by means of tension bolts of hollow design. However, it has become evident that in more-modern vacuum-assisted brake-force boosters the tension bolts are to be omitted more and more, and that only corresponding fastening bolts, which do not extend right through the booster housing, are fitted to the outside of the booster housing.
By way of further document pertaining to the state of the art, reference is made to U.S. Pat. No. 6,772,674 B2, which is incorporated by reference herein. This document likewise presents a vacuum-assisted brake-force booster with tandem chamber arrangement, the two working chambers being pneumatically connected to one another via a tubular element. The tubular element is tightly fitted to the booster housing, whereby the first movable wall, which separates the first working chamber from the first vacuum chamber, is able to slide on this tubular element in mobile manner. A similar solution is known furthermore from document U.S. Pat. No. 6,588,317 B2 and also from document U.S. Pat. No. 6,755,117 B2.